Well, there is a reason. Dropping ball joint under arm you going from uber-strong setup, practically bomb prof, to fairly marginal. If you plan to do anything serious with you truck I would be pretty cautious. Street cruising is OK. Otherwise you open up to potentially ripping ball joint off upper arm and/or CV popping out of hub or differential.
I've seen both happen. First one is definitely more disastrous.

92 SR, 285/75R16 Yoko MT ARB locker GAST compressor AirLift 1000 MM10500 Snorkel custom rear bumper
02 Montero LS died protecting the master
08 PowerWagon (stock!)